The authorities instruct operators of gas pipelines to operate the lines so that the risk of a gas leakage during a one-year period lies within a given safety level. The authorities' required instructions will vary from country to country, but will in all cases impose instructions as to how a gas pipeline shall operate. A typical safety level is that the yearly probability of a leakage and to exceed a given pressure within a margin of 2 bar, shall be less than 1×10−3, total for all sources for high pressure and all incidents, which may occur during the operation of the pipeline. In order to comply with the instructions, a safety device or safety unit is arranged in connection with the pipeline. The components, which may be used in connection with the safety device, must be approved by the authorities to have a reliability that meets the safety level. A crucial consideration in connection with the current invention is that the gas pipeline and all of the equipment determining safety must be within a given total safety level, which is why it is not relevant to use methods or components that are not approved for that safety level. There are a number of process control systems and leakage detection systems which are not useful in relation with a safety device in connection to a gas pipeline.
Prior known safety devices for gas pipelines make use of pressure and temperature measurements. There are no previously known safety devices which also make use of measuring the flow rate at the inlet of the gas pipeline. The gas' compressibility does not provide an immediate correlation between the flow rate, pressure and temperature in to the pipeline in relation to what is transmitted out of the pipeline. This is why safety devices suitable for a liquid conducting pipeline are not functional for a gas conducting pipeline.
In a typical instance, the gas pipeline shall be connected to an existing pipeline system, and the supplying pressure for the gas from the pipeline through an outlet must not exceed a given threshold value, decided by requirements given for the receiving pipeline system. The connecting of the pipeline and the pipeline system is typically carried out with a so-called hot tap connection. There is a need for a gas pipeline, which is particularly suitable for connecting to an existing pipeline system in accordance with the requirements as mentioned above.